1. Field of the Invention
The invention concerns a method for correction of the pixels of an x-ray image data set.
2. Description of the Prior Art
X-ray apparatuses have a storage or image plate, for example, as an x-ray detector. This can be a substrate on which an x-ray storage luminophore layer is deposited. Such an image plate is typically arranged in a cassette. The x-ray radiation attenuated upon penetration through the examination subject interacts with the storage film as an x-ray intensity distribution and is absorbed thereby. Electrons in luminophore crystals are thereby converted into an excited, meta-stable state. The electrons located in an excited, meta-stable state are excited again by photo-simulation and consequently revert to their ground state. Light proportional to the x-ray intensity distribution is thereby emitted and detected with a readout device that is suitable and known to those skilled in the art from, for example, Schulz, Forschungsbericht Röntgenstrahlung 2001 (173), pages 1137-1146. A computer downstream from the readout device calculates an x-ray image data set from the read data.
The sensitivity of the storage film can be inhomogeneous, such that given exposure of the image plate with a homogeneous x-ray intensity distribution the corresponding x-ray image exhibits different grey values. In order to compensate the inhomogeneous sensitivity of the storage film, the individual pixels of the x-ray image data set can thus be corrected (and in particular normalized) with respective correction values associated with one of the individual pixels. The individual correction values can be experimentally determined, for example, for an individual image plate before its delivery and be stored once on a data memory of the readout device.
Given specific materials for the storage film, the sensitivity with the accumulated x-ray radiation to which the storage film is exposed can change. Such materials are, for example, doped alkali halogenide, for example KBr, Rbl, RbBr, CSBr doped with IN, Ga, TL and/or Eu. Since the x-ray radiation is attenuated by the examination subject, the applied x-ray doses of the individual sub-regions of the storage film differ. For example, the boundary regions of the storage film are thus normally exposed to a higher x-ray dose than regions near the middle of the storage film. In general, the accumulated x-ray doses of the individual sub-regions of the storage film thus differ. The sensitivities of the sub-regions of the storage film consequently also change differently with time, i.e. with the number of x-ray image data sets produced.